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When should I install the secondary grounding cable to my rack automatic transfer switch ?


This article outlines our recommendations in regards to installing the secondary grounding cable to the rack Automatic Transfer Switch (ATS) units.  Although the ATS has a a leakage of less that 3.5 mA the combined  load switched by the ATS exceeds this value.  For this reason extra earthing (Grounding) is required.

Product Line
  • AP44XX series Automatic Transfer Switches (AP4421, AP4433, AP4422, AP4423, AP4434, AP4424, AP4430, AP4431, AP4432, AP4450, AP4452, AP4452J, AP4453).

  • All Firmware revisions.


Customers looking to clarify the information available in the Installation and quick start manual.


If the total measured leakage current exceeds 3.5mA we recommend to attach a ground wire from the Rack ATS supplementary ground (M4 thread) to a reliable ground connection before energizing the Rack ATS.
The value of 3.5mA is in conformance with IEC/EN 60950 clause 5. The leakage current value of the ATS without loads installed is below the limits required in Table 5A of the standard. The supplementary chassis ground terminal connection is recommended for installations to the meet their requirements if the known or measured leakage current exceeds 3.5mA.

APC Czech Republic

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